The field of the present disclosure relates generally to composite structures and, more specifically, to filler materials for composite structures that facilitate restricting delamination of the composite structure.
Cracking of integrally stiffened composite structures, especially in aerospace applications, often initiates in a radius filler (i.e., noodle) located at an interface between a skin and integral stiffening elements of the composite structures. At least some known radius fillers are formed at least partially from an amount of resin. Cracks in the resin may form during manufacture of the composite structures as a result of improper tooling, improper handling of tools, and/or residual tensile strain. For example, residual tensile strain in composite structures may form as a result of a mismatch between the coefficients of thermal expansion creating a strain environment in the radius filler that exceeds the critical cracking strain of the resin. The geometry of the structure surrounding the radius filler creates a three-dimensional constraint to shrinkage upon cooling of the resin after it has been cured and hardened.
Exemplary radius filler materials include, but are not limited to, pre-impregnated (i.e., prepreg) composite materials (e.g., layered strips and/or rolled prepreg composite material), and/or pure resin. In at least some known composite structures, crack propagation in the radius filler can cause delamination of the plies in adjacent laminated joints. More specifically, crack propagation in the radius filler may initiate degradation of the laminated joints. While limiting the formation of cracks in the radius filler would ensure the integrity of the laminated joints, preventing cracks from forming entirely is generally difficult, if not impossible. Moreover, the difficulty in limiting crack formation in radius fillers increases as composite structures are fabricated in increasingly large sizes. As such, there is a need for systems and methods that ensure cracks in a radius filler do not initiate degradation of laminated joints.